<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes" />
    <title>ShellCheck: SC2149 – Remove `$`/`${}` for numeric index, or escape it for string.</title>
    <link rel="stylesheet" href="css/bootstrap.min.css" />
  </head>
  <body style="margin-left: auto; margin-right: auto; max-width: 800px">
    <h1>SC2149 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC2149">See this page on GitHub</a>
    <p style="display: none"><a href="index.html">Sitemap</a></p>
    <hr />
    <h2 id="remove--for-numeric-index-or-escape-it-for-string">Remove
<code>$</code>/<code>${}</code> for numeric index, or escape it for
string.</h2>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC2149.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="co"># Regular array</span></span>
<span id="cb1-2"><a href="SC2149.html#cb1-2" aria-hidden="true" tabindex="-1"></a><span class="va">index</span><span class="op">=</span>42</span>
<span id="cb1-3"><a href="SC2149.html#cb1-3" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="va">$((array</span><span class="op">[</span><span class="va">$index</span><span class="op">]</span><span class="va">))</span></span></code></pre></div>
<p>or</p>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC2149.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="co"># Associative array</span></span>
<span id="cb2-2"><a href="SC2149.html#cb2-2" aria-hidden="true" tabindex="-1"></a><span class="va">index</span><span class="op">=</span>banana</span>
<span id="cb2-3"><a href="SC2149.html#cb2-3" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="va">$((array</span><span class="op">[</span><span class="va">$index</span><span class="op">]</span><span class="va">))</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<pre><code># Regular array
index=42
echo $((array[index]))</code></pre>
<p>or</p>
<div class="sourceCode" id="cb4"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb4-1"><a href="SC2149.html#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="co"># Associative array</span></span>
<span id="cb4-2"><a href="SC2149.html#cb4-2" aria-hidden="true" tabindex="-1"></a><span class="va">index</span><span class="op">=</span>banana</span>
<span id="cb4-3"><a href="SC2149.html#cb4-3" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="va">$((array</span><span class="op">[</span><span class="dt">\$</span>index<span class="op">]</span><span class="va">))</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>For a numerically indexed array, the <code>$</code> is mostly
pointless and can be removed like in <a href="SC2004.html">SC2004</a>.</p>
<p>For associative arrays, the <code>$</code> should be escaped to avoid
accidental dereferencing:</p>
<div class="sourceCode" id="cb5"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb5-1"><a href="SC2149.html#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="bu">declare</span> <span class="at">-A</span> <span class="va">array</span></span>
<span id="cb5-2"><a href="SC2149.html#cb5-2" aria-hidden="true" tabindex="-1"></a><span class="va">index</span><span class="op">=</span><span class="st">&#39;$1&#39;</span></span>
<span id="cb5-3"><a href="SC2149.html#cb5-3" aria-hidden="true" tabindex="-1"></a><span class="va">array</span><span class="op">[</span><span class="va">$index</span><span class="op">]=</span>42</span>
<span id="cb5-4"><a href="SC2149.html#cb5-4" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&quot;</span><span class="va">$((</span> <span class="va">array</span><span class="op">[</span><span class="va">$index</span><span class="op">]</span> <span class="va">))</span><span class="st">&quot;</span>    <span class="co"># bash: array: bad array subscript</span></span>
<span id="cb5-5"><a href="SC2149.html#cb5-5" aria-hidden="true" tabindex="-1"></a><span class="bu">echo</span> <span class="st">&quot;</span><span class="va">$((</span> <span class="va">array</span><span class="op">[</span><span class="dt">\$</span>index<span class="op">]</span> <span class="va">))</span><span class="st">&quot;</span>   <span class="co"># 42</span></span></code></pre></div>
<h3 id="exceptions">Exceptions</h3>
<p>None.</p>
    <hr />
    <p style='font-size: 80%'><a href="../index.html">ShellCheck</a> is a static analysis tool for shell scripts. This page is part of its documentation.</p>
  </body>
</html>


